In general, this invention relates to a color video printer for producing a color photographic copy from a color video signal. In particular, this invention relates to a color video printer in which a color video signal is modified with additional gain in the near white region of the signal to compensate for the decreasing sensitivity in the near white region of a self-processing photographic element.
Several techniques have been proposed to make a color copy from a color video signal. If a still camera is used to directly photograph an image displayed on a color video monitor, difficulties arise which result in poor copy quality such as in synchronizing the shutter speed of the camera with the field rate of video image displayed on the monitor and in positioning the camera relative to the monitor screen. Moreover, there is no simple method to compensate for the relative insensitivity of the photographic material in the near white region. Another proposed video printing technique divides the color video signal into red, blue and green component video signals which are sequentially displayed on a monochrome monitor (See e.g., U.S. Pat. Nos. 4,473,849 and 4,468,693). The screen of the monitor is photographed through stationary color filters corresponding to the color component signal applied to the monitor. This technique is time consuming since color film is exposed to several video frames of each color component signal. Although the apparatus disclosed in the referenced patents provide for adjustment of the video signals prior to exposure in order to compensate for exposure characteristics of the copy film, such adjustments are effected with complex and expensive analog or digital circuitry.
In cross-referenced, copending U.S. patent application Ser. No. 776,232, entitled COLOR VIDEO PRINTER, there is disclosed a compact, easy to use and economical color video printer which provides a full resolution copy of a color video signal in short exposure and processing time. As disclosed, a self-processing color photographic element is exposed to a sequence of six color field images constituting a full frame of a color video image. The color images are produced by a monochrome cathode ray tube (CRT) and a rotatable filter having red, green and blue filters which are sequentially moved at field frequency into an optical path between the CRT and the photographic element. A video signal circuit provides a color video signal including concurrent red, green and blue component signals. A selectively actuated gate applies one of the color component signals to the CRT to effect exposure of the photographic element.
In such a color video printer, it is desirable to provide a simple and inexpensive technique for modifying the color component signal applied to the CRT, in order to compensate for the decreasing sensitivity in the near white region of the self-processing photographic element. It is also desirable to provide for simple and inexpensive controls to adjust the relative amount of red, green and blue signal contributing to the photographic exposure in order to compensate for variability in CRT phosphor characteristics from printer to printer.